The invention relates to improvements in brake boosters for vehicles. This application is being filed concurrently with Ser. No. 189,893, for related subject matter, further identified by R. 21201. German patent application P 37 15 564.4 has already described such a brake booster, which replaces the valves provided in known brake boosters. The present exemplary embodiment is intended to contribute further to improving the closing of the valves in the brake booster, and in particular to facilitate centering the valves.